The results of nonempirical self-consistent band structure LMTO calculations of the electronic properties of B1-like solid solutions in Ti-Al-N-C and Ti-Si-N-C systems are given. The regularities of changing the electronic and energy parameters of solid solutions as a function of their composition are discussed. Direct Computer modelling of the influence of the possible, mechanisms of solid solution formations (according to Al, Si → C, N or Al, Si → Ti substitution types) on their band structure is carried out. The effect of oxygen impurities and nitrogen lattice vacancies on the electronic properties of the considered solid solutions is discussed taking Ti silicidonitride as an example. The results obtained are compared with recent XPS investigations of metastable B1-TiSixNy(O) films.